This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A decade ago, research published in Pediatrics revealed that young girls were developing pubertal changes earlier than had been described in textbooks. Currently, preliminary data suggest that boys also may be starting to develop physically earlier than in the recent past but the validity of these findings is uncertain. The Secondary Sexual Characteristics in Boys (SSCIB) study will determine the stages of secondary sexual development and mean ages of onset of pubertal testicular enlargement among boys of varied racial and ethnic origin seen in pediatric practices in the U.S. today. Nearly, 7000 boys ages 6 through 16 years will be studied. This is a Prospective, Observational, Population-Based Study (based on participating providers). This study will aid in developing appropriate clinical standards by race/ethnicity for assessing typical growth and development in U.S. boys. This study will provide a basis for future studies by using Tanner Staging and Testicular Measurement (orchiometer) in early puberty, which will provide data for following secular trends. All males, aged 6 through 16 years who are seen in the UNM Pediatrics clinic for regular, well-child appointments with participating providers, will be screened for eligibility for enrollment. The projected number for UNM is 660 enrolled (Based on an estimated 22 participating providers at UNM, who each plan to enroll 30 subjects). The projected total number at multiple sites is 6600.